Hardly a week goes by now without news of a pay dispute or potential strike action in the voluntary sector. Last week, for example, Scottish social care charity Quarriers was hit by strikes organised by the Scottish branch of the trade union Unison.
No sooner had the Quarriers strikers put down their banners in protest at below-inflation pay rises than Charity Commission workers picked up theirs in preparation for yesterday's national civil service strike, organised by the Public and Commercial Services Union.
Although these cases are hardly on the same scale as the miners' strikes of the 70s and 80s, they are not anomalies either. In fact, Michael Sippit, a senior employment solicitor at the law firm Clarkslegal, believes they are a sign of things to come.
"Over many years now, we have seen a lot of outsourcing from the public sector," he says. "We then get situations in which public sector employees are transferred in significant numbers to the private and voluntary sectors with their union agreements in place."
Sippit says that a substantial loosening of employment regulations since the turn of the century has allowed unions and elected employee representative bodies to increase their influence.
"Unions now have a legal right to be recognised if they have sufficient support in organisations," he says. "If a third sector organisation inherits a union agreement, it can't simply derecognise that union."
The Information and Consultation of Employees Regulations 2004 stipulate that any organisation with more than 100 employees has to consult elected representatives of the workforce if staff so request.
Mike Short, national officer for the voluntary and community sector at Unison, agrees there has been a growing unionisation of the sector.
"The voluntary sector is one of the fastest-growing in terms of Unison membership," he says. "This is partly because public sector members are transferring, but also because, as voluntary sector employers take on more core public services - often on short-term contracts - people feel their jobs are more vulnerable."
A Third Sector Online poll in April found that 85 per cent of readers think unionisation of charities is a good thing. But for some in the sector, this is a worrying trend.
"Most union officials are very antipathetic towards the third sector," says Stephen Bubb, chief executive of Acevo, the membership organisation for charity directors. "They're very critical and they don't know much about us."
Bubb accepts that unionisation of the sector is becoming inevitable, but he believes unions should take a softer approach towards charities because of the altruistic nature of the sector and the fact that many organisations deal with vulnerable clients.
"The whole concept of having a strike among voluntary sector staff is very damaging to the wider community," he says. "It's simply not appropriate."
But Sippit believes charity bosses must wake up to the reality of union engagement.
"It is imperative that third sector organisations begin to have more clarity about the rights of unions, what they as employers can be sued for and how industrial disruption might affect their obligations to public sector contractors," he says.
He advises charities to revise their human resources strategies so that management addresses the collective concerns of the workforce, not just those of individual employees.
He says they also need to know about their liabilities if, for example, they take on public sector staff who are engaged in equal pay disputes with their previous employers.
"The charity inherits the liability of that equal pay claim, with all of the back-pay implications," Sippit warns.
Finally, he says, when charities are drawing up public service contracts with local authorities, they should ensure they won't be liable if strikes bring services to a halt.
According to Short, however, the sector's relationship with unions need not be a hostile one. He says unions can actually help employers to meet the training and development needs of their staff, and they can also assist an organisation in avoiding strikes or litigation when a disagreement arises.
"We're interested in entering into partnerships with employers," he says. "That doesn't mean we'll agree on everything, but it does mean we can agree a mechanism for when there are disagreements.
"We try to seek common ground and we try to understand where the other party is coming from."